In recent years, with the development of high-properties and networking of computer and information communication equipment, to reach high-speed transmission and deal with large-capacity information, operation signals tend to be high-frequency. Therefore, the material of the circuit substrate material must be improved.
Among the conventional materials used for the printed circuit substrate, epoxy resin with excellent adhesion characteristics is widely used. However, the epoxy resin circuit substrate has a relatively high dielectric constant and a dielectric loss tangent (dielectric constant is more than 4, dielectric loss tangent is around 0.02), and inadequate high-frequency characteristics, which results in failure to meet the requirement of high-frequency signals. Therefore, it is necessary to use resins with excellent dielectric properties i.e., the resin must have a low dielectric constant and dielectric loss tangent. For a long time, technicians in the field have studied thermosetting polybutadiene or butadiene copolymer resins with excellent dielectric properties. The results of these studies are cited as follows:
European patent application No. WO97/38564 discloses the use of nonpolar styrene-polybutadiene divinyl benzene terpolymer added with magnesium aluminum silicate as a filler, and the use fiberglass cloth as a reinforcing material to make a circuit substrate which has excellent dielectric properties but poor peel strength.
U.S. Pat. No. 5,571,609 discloses the use of 1,2-polybutadiene resin or polyisoprene with a molecular weight of less than 5,000, and nonpolar butadiene styrene copolymer with a high molecular weight, with silica as a filler, and the use of fiberglass cloth as a reinforcing material to make a circuit substrate which also has excellent dielectric properties but poor peel strength.
U.S. Pat. No. 6,569,943 discloses the use of amine modifer polybutadiene liquid resin with vinyl added with monomers of low molecular weight as a curing agent and diluent, and the use of impregnated fiberglass cloth to make a circuit substrate. Although the dielectric properties and peel strength are excellent, the resin system is liquid at normal temperature, and so can not be made into a tack-free prepreg. Therefore, in the compression molding of a sheet, it is difficult to adopt common stacked technology of the prepreg, which results in a difficult process operation.
Among the above-mentioned disclosures, the resin used in the first two patents is a non-polar resin material. Although the resulting circuit substrate has excellent dielectric properties and high-frequency properties, the molecular structure of the resin material not have polarity groups to help improve the adhesion properties, making the adhesiveness of the circuit substrate copper foils poor (peel strength less than 0.8 N/mm). In the fabrication process of the circuit substrate, the circuit substrate must withstand high-temperature or reflow welding, and the low peel strength of the copper foil reduces reliability and increases the risk of the failure of circuits. In addition, the other patent discloses the use of an amine modifer polybutadiene liquid resin with vinyl in the end having polarity groups in the molecular structure to improve the peel strength. However, it does not solve the tackiness problem of the liquid resin, and so does not make a prepreg which is convenient to operate, which results in poor process operability.